This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Interest in the mechanism of action for natural peptide-antibiotics has expanded due to the increased resistance of pathogens to currently employed antibiotics. It is assumed that amphiphatic helical peptide-antibiotics are acting by lysis of the bacterial cell membrane or by pore formation. Disruption of the cell membrane is generally thought to be a principal method to kill microbial cells or at least to inhibit of their growth. However, direct spectroscopic evidence for the occurrence of pore forming aggregates of helical molecules in phospholipid membranes is still lacking. In spite of this, it is known that peptides, which are long enough to span the bilayer can penetrate the phospholipid bilayer with the formation of the trans-membrane configuration, for which a single trans-membrane helix would be energetically unfavorable. For this reason the barrel-stave model of ion channel formation is still of interest to study, but with techniques (PELDOR/ESEEM) which have not been used before. Recently, we have studied peptide aggregation of the 19-mer peptide alamethicin by means of the PELDOR technique. In this way we could determine aggregate formation, the number of monomeric molecules per aggregate and the intermolecular distances between the monomers of the aggregate as well. This technique was also found to be a powerful tool to study the location and distribution of peptide molecules in the natural and artificial membranes. However, so far we have not determine the channel aggregate structure in the membranes. This will be the aim of our studies in this project. ACERT has the unique collection of ESR instruments and technique, which exists only at Cornell University. Practically all of these instruments can benefit our research in the following areas outlined in the scientific program of ICKC: a)investigations of biologically important systems by means of dipolar spectroscopy;b) Investigations of physical dynamics in these objects. c) development and improvement of new experimental techniques for these studies.